As a quick pointer ... the barrier to full-disk encryption issue is the root (/) partition. The available solution(s) will likely pivot on whether you can or cannot tolerate an un-encrypted root partition.

/S

__________________Never argue with an idiot. They will bring you down to their level and beat you with experience.

Are you sure? Because i had to modify /etc/sysctl.conf to turn in on in 4.6.

Code:

#vm.swapencrypt.enable=0 # 0=Do not encrypt pages that go to swap
to
vm.swapencrypt.enable=1 # 0=Do not encrypt pages that go to swap

Man you have to do some reading before asking. Default behavior of OpenBSD box is opposite of what is commented in systct.conf. Those lines are
left like that so that if you want to turn off swap encryption you can just remove # and reboot the computer.